Figure 5.

Enzymatic hydrolysis of poly[U] caused a transient increase in the rate of oligonucleotide-induced channel blockades. In two separate experiments, at time 0, ribonuclease A (bovine pancreatic RNase Type XII-A; Sigma or Worthington) was added to the cis chamber containing either 0.13 mg/ml poly[U] (•) (mean length, 1100 nt) or 0.27 mg/ml poly[A] (□) (mean length, 20,000 nt; Fluka). The final ribonuclease concentrations were 0.04 mg/ml (poly[U] experiment) or 0.13 mg/ml (poly[A] experiment). Blockade rates were calculated from single channel recordings. The Inset shows (null)/1;3-sec sample traces for the poly[U] experiment before (Upper) and ≈30 sec after (Lower) addition of ribonuclease. Similar experiments with a poly[U] sample of greater length (3000 nt) yielded results comparable to those obtained with the 1100-nt poly[U]. The current was digitized using a SONY/Dagan DAT recorder at 48,000 points/sec.